Autodetect xlinks when creating sync view
To avoid mistakenly adding multiple xlink targets to the same source when creating sync views and to make sync view creation to repos with xlinks easier I suggest that the sync view editor should be "target" centric, not "source" centric:
I click add new sync view.
Instead of clicking add new source as I am supposed to now, I click "add new target".
I choose the target on a target server.
Plastic detects that I already have a repo with the same name on my source server (or use some other similarity measure as I have suggested above) and ask if I want to use that source repo, another source repo or create a new.
Plastic detects that the target repo has xlinks. For each xlink Plastic repeats the above check for a source repo and offers to use that, another or a create a new.
By using a target first approach, this would eliminate the risk of the above error and be very convenient.
Combine that with a button for syncing all targets and you have a near perfect sync view system.